Recently, there have been prevailed a hybrid vehicle running concomitantly with an engine and an electric motor (hereafter referred to as HEV), or an electric vehicle running only with electric motor. For example, HEV is provided with a low-voltage battery about 12 V for starting the aforementioned electric motor and actuating electric components in the vehicle, and a high-voltage battery for driving the aforementioned electric motor. The aforementioned high-voltage battery includes secondary battery such as nickel hydride battery or lithium battery as unit cell (that is, battery cell) and has this unit cell connected in series in the plural to compose a battery pack so as to obtain high-voltage (see PTL 1 for example).
The aforementioned high-voltage battery has variation induced in a between-electrodes voltages of each unit cell, i.e., a state of charge (SOC) as repeating charge and discharge. Charge and discharge for high-voltage battery is required, in view of tolerance or safety of each unit cell, to prohibit charging when the unit cell with the highest between-electrodes voltage reaches a predetermined upper limit voltage, and to prohibit discharging when the unit cell with the lowest between-electrodes voltage reaches a predetermined lower limit. Therefore, in an abnormal state in which each unit cell induces variation of SOC, usable capacity of the battery is substantially reduced. Thereby, in the aforementioned high-voltage battery it is required that the unit cell with higher between-electrodes voltage is discharged separately from the aforementioned electric motor drive, and that the SOC of each unit cell is equalized to return to its normal state. In order to equalize the SOC of each unit cell, it is required to monitor the between-electrodes voltage of each unit cell.
Furthermore, as the aforementioned high-voltage battery generates a great deal of heat by discharging large current upon driving the electric motor, the battery, if a part of unit cell has such a defect, may lie in abnormal state of high temperature exceeding allowable upper limit temperature. Thereby, in order to obviate this abnormal state by stopping discharging before such abnormal state of high temperature arises, it is required to monitor temperature of the high-voltage battery. Furthermore, variation of the battery temperature has the aforementioned between-electrodes voltage varied, requiring compensation for the aforementioned between-electrodes voltage for temperature.
FIG. 16 illustrates a high-voltage battery system that is a conventional battery state monitoring system.
This high-voltage battery system (shown by reference sign 801 in the figure) is provided with a high-voltage battery 810 as a plurality of battery packs, a battery state monitoring device 850 monitoring a state of the high-voltage battery 810.
The high-voltage battery 810 is provided with a battery module 820 including a plurality of battery cells 821 arranged in one direction, a bus bar module 830 arranged overlaid on an upper face of the battery module 820, a wiring harness 840 including a connector plug 841 and a plurality of cables 842.
The bus bar module 830 is provided with a plurality of bus bars 831. The plurality of bus bars 831 has a plurality of battery cells 821 coupled in series entirely by connecting positive and negative electrodes of the battery cell 821 adjacent to each other. The bus bar module 830 is also provided with a plurality of temperature sensors 832 at a middle and both ends in the one direction (namely, arrangement direction of the plurality of battery cells 821) that outputs voltage in accordance with the measured temperature.
The plurality of cables 842 of the wiring harness 840 has one ends thereof each connected to not-shown terminals within the connector plug 841, and has the other ends thereof each connected to a plurality of terminal fittings 833 that are connected to electrode of the battery cell 821 as by overlaying on the plurality of bus bars 831, and the aforementioned temperature sensor 832.
The battery state monitoring device 850 is provided with, for example, a box-type case 851, a controller (not shown) composed of such a microprocessor housed in the case 851. The case 851 is provided with a connector socket (not shown) adapted to engage with the connector plug 841 of the wiring harness 840 that is exposed from the case 851. Engagement of the aforementioned connector plug 841 with the connector socket allows the controller and the wiring harness 840 (that is, the aforementioned terminal fitting 833 and the aforementioned temperature sensor 832) to connect.
Thereby, the controller, in accordance with a voltage outputted from the plurality of terminal fittings 833 and the aforementioned temperature sensor 832, detected temperature of the between-electrodes voltages of the plurality of battery cells and the battery cell, and monitored whether each battery cell 810 lies in normal state or not.
Disadvantageously, the aforementioned high-voltage battery system 801 needed a number of plurality of cables 842 according to that of battery cell 821, and needed a enlarged space for wiring the wiring harness 840 because of the plurality of cables 842 being pulled out of the battery cell 821 and being wired to the battery state monitoring device 850 as it is, resulting in difficulty of wiring design and wiring work. Furthermore, while the electrode voltage of the battery cell 821 is inputted to the battery state monitoring device 850 via the wiring harness 840, this electrode voltage of this battery cell 821 may become high-voltage of several hundred volts in potential difference from reference potential such as car body, requiring design for safety/reliability such as insulation resistance or noise resistance in view of mixture of high-voltage as such and low-voltage for controlling, which made it difficult to design electrically such devices.
Thereby there has been advocated as a configuration to resolve these problems a battery state monitoring system as shown in FIG. 17 (shown by reference sign 901 in the figure).
The battery state monitoring system 901 is provided with a battery pack 910 as a plurality of battery packs, a battery state monitoring unit 960 monitoring the state of the plurality of battery packs 910, a wiring harness 970 connecting the plurality of battery packs 910 and the battery state monitoring unit 960.
The battery pack 910 is provided with a battery module 920 composed of a plurality of battery cells 921 arranged in line, a plurality of bus bars 932, a plurality of terminal fittings 933, and a bus bar module 930 including a plurality of temperature sensors 934 and a battery state notifying unit 940. In the bus bar module 930 disposed to each battery pack 910, the battery state notifying unit 940 generates a battery state data in accordance with a cell temperature signal according to a voltage outputted from the cell voltage signal and the temperature sensor 934 that is based on the between-electrodes voltages of the battery cell 921 outputted from the terminal fitting 933 of the battery pack 910, which the battery state data is composed of a digital signal including data indicating between-electrodes voltages and temperature of the battery cell 921, and transmits the battery state data to the battery state monitoring unit 960.
It follows from this that in the battery state monitoring unit 960, the state of the battery pack 910 can be monitored based on the battery state data transmitted from the battery state notifying unit 940 of each battery pack 910, and thereby it is made possible to reduce the number of the plurality of cables in the wiring harness 970 connecting the battery state notifying unit 940 and the battery state monitoring 960, and to facilitate wiring design and wiring work for the wiring harness 970. Furthermore, transmission of the aforementioned battery state data composed of the digital signal to the battery state monitoring unit 960 makes it possible to reduce the signal to be transmitted to lower voltage of the order of several volts, facilitating electrical design for safety/reliability such as insulation resistance or noise resistance to the battery state monitoring unit 960.